The switching latency of packet switching equipment is a key competitive product feature. For example, Ethernet switch vendors currently advertise latencies on the order of nanoseconds. Because switching latency is an important product feature, switch manufacturers require a mechanism to accurately measure switching latency of their devices.
In general, the switching latency of a switch is a measure of how long it takes the switch to switch a packet from an ingress port of the switch to an egress port of the switch. Thus, a switch manufacturer may test the latency of a device, such as an Ethernet switch, by transmitting packets to the switch, determining when the packets are received from the switch, and calculating the difference between packet transmit and receive times. The average latency value, median latency value, mode latency or other statistical measure of latency derived from the tests may be reported or advertised as a product feature.
In some operational scenarios, the switching latency of a switch may increase beyond the advertised or rated value. Increases in switching latency beyond the advertised or rated latency value may be caused by improper buffering by the switch due to overloading of resources within the switch. However, another cause of switching latency that is not caused by improper buffering is buffering due to transmission of virtual lane markers or identifiers. Virtual lane markers are transmitted by packet switching devices to identify the lane with which the group of packets is associated. In 100 gigabit Ethernet, a compliant device is required to transmit a virtual lane marker or identifier of 160 bits every 207 microseconds. If a test device transmits a packet to a device under test, and the packet is received when the device under test is required to send a virtual lane marker, the measured latency of the device under test will increase even though the increase in latency is not caused by improper buffering by the device under test. It is desirable to account for the effect of virtual lane marker transmission on device latency. Accordingly, there exists a need for improved methods, systems, and computer readable media for precise measurement of switching latency of packet switching devices.